[PATCH 2/4] hurd: Implement MSG_CMSG_CLOEXEC

[Sergey Bugaev]

This is a new flag that can be passed to recvmsg () to make it
atomically set the CLOEXEC flag on all the file descriptors received
using the SCM_RIGHTS mechanism. This is useful for all the same reasons
that the other XXX_CLOEXEC flags are useful: namely, it provides
atomicity with respect to another thread of the same process calling
(fork and then) exec at the same time.

This flag is already supported on Linux and FreeBSD. The flag's value,
0x40000, is choosen to match FreeBSD's.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---
 sysdeps/mach/hurd/bits/socket.h | 5 ++++-
 sysdeps/mach/hurd/recvmsg.c     | 3 ++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/sysdeps/mach/hurd/bits/socket.h b/sysdeps/mach/hurd/bits/socket.h
index 2d78a916..c2392bed 100644
--- a/sysdeps/mach/hurd/bits/socket.h
+++ b/sysdeps/mach/hurd/bits/socket.h
@@ -197,8 +197,11 @@ enum
 #define MSG_WAITALL MSG_WAITALL
     MSG_DONTWAIT       = 0x80, /* This message should be nonblocking.  */
 #define MSG_DONTWAIT MSG_DONTWAIT
-    MSG_NOSIGNAL       = 0x0400        /* Do not generate SIGPIPE on EPIPE.  */
+    MSG_NOSIGNAL       = 0x0400,       /* Do not generate SIGPIPE on EPIPE.  */
 #define MSG_NOSIGNAL MSG_NOSIGNAL
+    MSG_CMSG_CLOEXEC   = 0x40000       /* Atomically set close-on-exec flag
+                                          for file descriptors in SCM_RIGHTS.  
*/
+#define MSG_CMSG_CLOEXEC MSG_CMSG_CLOEXEC
   };
 
 
diff --git a/sysdeps/mach/hurd/recvmsg.c b/sysdeps/mach/hurd/recvmsg.c
index 5e8b18c6..56c163fe 100644
--- a/sysdeps/mach/hurd/recvmsg.c
+++ b/sysdeps/mach/hurd/recvmsg.c
@@ -195,11 +195,12 @@ __libc_recvmsg (int fd, struct msghdr *message, int flags)
 
        for (j = 0; j < nfds; j++)
          {
+           int fd_flags = (flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
            err = reauthenticate (ports[i], &newports[newfds]);
            if (err)
              goto cleanup;
            fds[j] = opened_fds[newfds] = _hurd_intern_fd (newports[newfds],
-                                                          0, 0);
+                                                          fd_flags, 0);
            if (fds[j] == -1)
              {
                err = errno;
-- 
2.39.2